1. Field of the Invention
The present invention relates to a cassette-type radiographic apparatus having photoelectric conversion elements.
2. Description of the Related Art
Conventionally, radiographic systems have been widely used in the fields of industrial nondestructive detection and medical diagnosis. In such systems, radiation is emitted to a subject from a radiation generation means, and the intensity distribution of the radiation that has been transmitted through the subject is detected by radiation detection means in order to obtain the radiographic image of the subject. These systems use a method of taking a photograph with the combination of a photosensitive film and a fluorescent substance, that is, a commonly-called film/screen method. In this film/screen method, a rare-earth fluorescent substance, which emits light when radiation is emitted, is formed into sheets, which are held in close contact with both sides of a photosensitive film. Radiation, which has been transmitted through the subject, is converted into visible light by the fluorescent substance. This visible light is captured by the photosensitive film, and a latent image formed on the photosensitive film is developed by a chemical process so as to be made visible.
With advances in digital technology in recent years, a radiographic image recording/reproduction system, which uses a method of converting a radiographic image into an electrical signal, is proposed in Japanese Unexamined Patent Application Publication Nos. 55-12429 and 56-11395. In this proposed type of system, a radiographic image is converted into an electrical signal, which is subjected to image processing. The signal is reproduced as a visible image on a CRT, etc., and a high-quality radiographic image is obtained. Then, when the radiographic image is converted into an electrical signal, the intensity distribution of the radiation which has been transmitted through the subject is temporarily stored as a latent image in the store-type fluorescent substance. Thereafter, fluorescence corresponding to the latent image, which is created by irradiating exciting light such as laser light to the fluorescent substance, is photoelectrically read, and this is output as a visible image.
Furthermore, with advances in the semiconductor processing technology, a radiographic system using a semiconductor sensor has been developed. This type of system has a dynamic range which is very large compared to conventional radiographic systems using a photosensitive film, and has a practical advantage that a radiographic image which is not susceptible to variations of the amount of exposure of radiation can be obtained. Furthermore, since this type of system, unlike conventional systems that use a photosensitive film, does not require a chemical process, an output image can be obtained instantly.
Such a radiographic system using a semiconductor sensor comprises radiation generation means for irradiating a subject, radiation detection means for detecting the radiation which has been transmitted through a subject, image processing means for performing digital processing on an image signal from the radiation detection means, and display means for displaying a radiographic image. The radiation generation means comprises a plurality of photoelectric conversion elements arranged in a two-dimensional lattice shape, and is disposed in a radiographic room together with the radiation generation means.
Presently, to quickly photograph a wider range of portions of a subject, as radiation generation means, a radiographic device which is thin, lightweight, and portable, that is, a so-called “electronic cassette”, has been developed. For example, as shown in FIG. 11, disposed inside a housing 2 of an electronic cassette 1 are: a fluorescent substance 3 for converting radiation into visible light; a photoelectric conversion element 4, arranged in a lattice shape, for converting visible light into electrical signals; a substrate 5 on which the photoelectric conversion element 4 is formed; a base 6 for supporting the substrate 5; a circuit substrate 7, having an electronic component 7a, for processing an electrical signal; and wiring 8 for electrically connecting the photoelectric conversion element 4 to the circuit substrate 7.
When this electronic cassette 1 is used, the operator varies the manner in which the electronic cassette 1 is disposed in accordance with the part of the subject to be photographed. For example, when the limbs of the subject are to be radiographed, the electronic cassette 1 is disposed horizontally on the floor, etc., and the portions of the subject to be photographed are placed on the top surface thereof. When the axial image of the shoulder joint of a subject S is to be radiographed, the electronic cassette 1 is held under the arm of the subject S as shown in FIG. 12, and radiation R is radiated from the opposing side (from above).
Next, referring to FIG. 15, the construction of another example of a conventional electronic cassette is described. FIG. 15 is a side sectional view of an example of a conventional electronic cassette. This electronic cassette 400 comprises: an image capturing element 451 formed of a fluorescent substance 451a for converting X rays into visible light, a plurality of photoelectric conversion elements 451b, arranged in a lattice shape, for converting the visible light into an electrical signal, and a board 451c on which the photoelectric conversion elements 451b are formed; a base 452 for supporting the board 451c; a circuit board 453 on which an electronic component 453a for processing a photoelectrically converted electrical signal is mounted; wiring 454 for electrically connecting the photoelectric conversion elements 451b to the circuit board 453; a power-supply circuit 460; power wiring 461 for supplying power to the photoelectric conversion elements 451b and the circuit board 453; and a housing 455 for these. The power-supply circuit 460 specifically comprises, for example, a combination of a battery and a DC/DC power-supply circuit, or a DC/DC power source for generating various voltages as a result of a predetermined voltage being externally supplied by a power-supply cable (not shown), etc.
When compared to a conventional photosensitive-film-built-in cassette, there is a possibility that as the weight increases, such an electronic cassette will be destroyed if it is inadvertently dropped. Therefore, it is thinkable that a handle should be mounted to the cassette for the purpose of reducing the likelihood of it being dropped, or the like.
For example, a handle mounted to a cassette which houses a storage-type fluorescent panel is disclosed in Japanese Unexamined Patent Application Publication No. 11-338079. In that patent application, a handle is provided on a side opposing the side from which the storage-type fluorescent panel is taken out, so that the cassette can be carried easily.
Furthermore, in Japanese Unexamined Patent Application Publication No. 06-342099, an electronic cassette having a handle mounted thereon so that the electronic cassette can be easily moved to an X-ray radiation position by hand is disclosed.
As described above, since the operator disposes the electronic cassette 1 horizontally on a floor, etc. or causes the electronic cassette 1 to be held under the arm of the subject, the electronic cassette 1 needs to be highly portable. Therefore, in order to improve the portability of the electronic cassette 1, in addition to the above-described known technologies, a bag-shaped electronic cassette 1′ in which an arm-shaped handle 9 is pivotably mounted to holes 2a formed in both sides of the housing 2 as shown in FIG. 13, and an electronic cassette 1″ in which a frame-shaped handle 10 is integrally provided on one end surface of the housing 2 as shown in FIG. 14 are thinkable.
Such electronic cassettes 1′ and 1″ do not pose problems when horizontally disposed on a floor, etc. However, when a specific portion of the subject is to be radiographed from a specific direction, for example, when the electronic cassettes 1′ and 1″ are held under the arm of the subject S as shown in, for example, FIG. 12, problems arise in that the handles 9 and 10 become obstacles to the subject S or the presence of the handles 9 and 10 makes it difficult to place the electronic cassette at a desired position. Therefore, it is preferable that the conventionally conceived electronic cassette 1 have high portability and be constructed so as not to decrease the degree of freedom of radiographing and so as not to cause the subject to feel discomfort.
The conventional examples described in the above-described publications disclose only that a handle is simply provided in a cassette so as to be suitable for carrying or moving the cassette, and do not disclose a construction in which a handle is attached to the electronic cassette by considering the specific properties of the electronic cassette. In particular, in the case of the electronic cassette, an important consideration is that there is a possibility that electronic parts, including semiconductor sensors, will be damaged by external impact.
And a consideration is that the electronic cassette has a construction in which a decrease of a signal-to-noise (S/N) ratio due to electromagnetic noise, etc., can be minimized. Also, a consideration is that the electronic cassette is convenient in that it is easy to hold, carry and position, and has convenience of radiographing, where a subject holds an electronic cassette and a radiograph is taken.